Determine the disease experience of the cohort over the ten year interval for analysis relative to baseline risk factor data. Validate the results of morbidity data obtained by previously mailed questionnaire. Ascertain a subgroup of MZ twins discordant for CHD incidence for analysis relative to differences in environmental factors. Estimate genetic variance for factors that were not collected in the initial examination, but may be related to the risk of CHD. Analyze data that were collected in the initial examination for verification of results of estimates of genetic variance.